The present invention relates to a position sensing apparatus. It should be understood that, while the specification describes the position sensing apparatus as being used in an apparatus for measuring the surface positions of an elongate article of manufacture, the position sensing apparatus of the present invention may find other applications.
It is often necessary to measure an elongate article of manufacture such as, for example, a beam or a tubular member to determine if there are errors in the formation of the article. This may involve testing the surfaces of the article to determine the extent the article bows or twists from its theoretical longitudinal axis. It should be understood that this testing or measuring is usually confined to articles of manufacture for which it is critical that the article be manufactured straight within predetermined specifications or tolerances. One such article of manufacture, for which the straightness of the article and its surfaces is critical, is a tubular coolant channel for use in nuclear fuel power reactors.
It is known to measure the surfaces of the article at predetermined intervals along its longitudinal axis by use of transducers and the like. The transducers are carried on a carriage which moves along a pair of guide rails. It is not economically practical however, to make the rails on which the carriage moves absolutely straight, and it is not practical to expect these rails to remain free of flaws once in use. Accordingly, this type of measuring apparatus, which uses a carriage movably mounted on a rail, does not compensate for any deviation of the carriage from its expected path of travel defined by the rails. The error introduced by the guide rails introduces inaccuracies into the measurement of the surface positions of the elongate article. The error introduced may be sufficient to render any measurement of the elongate apparatus by the transducers outside accepted tolerances.